1. Field of the Invention
The invention relates generally to hermetically sealed devices employing compressible and extendable bellows members for transferring the motion of an external control member to an internal movable member, and most particularly to vacuum and other hermetically sealed interrupters.
2. Description of the Prior Art
In the prior art extensive use has been made of axially extendable and compressible metallic bellows members, wherever the transfer of motion through the enclosure of a hermetically sealed device is required. That type of device broadly embraces the fields of vacuum and gas-filled capacitors and circuit breakers, those devices having long been employed in high voltage, high power applications because of the relatively favorable voltage breakdown characteristics afforded as compared to the same devices with air dielectric.
The invention is most particularly related to vacuum enclosure devices of the aforementioned general character, which encounter high acceleration, axial control movements such as vacuum breakers or interrupters as they are frequently called. In a vacuum interrupter, separation of the contacts is effected relatively violently in order that the delay in interrupting an over-current fault situation is minimized. Depending upon design and the nature of the controlling equipment, the closing action of a vacuum interrupted also might be accomplished in high velocity, high acceleration motion.
Since the bellows and related moving parts comprise a mass-compliance mechanical system, a typical series of masses connected by intervening springs may be thought of as schmatically representing the mechanical dynamics of the situation. The series of masses and intervening springs representing the bellows is anchored at one end corresponding to the fixed end of the bellows. When the movable end of such a system is rapidly accelerated in either direction, the forces operating on the masses must be transmitted through the springs. The usual metal bellows has an equivalent spring rate introduced by the resilience of the metal used, the latter being formed into a series of axially stacked convolutions. In such arrangements, the relatively large mass of the bellows system in relation to the spring rate of the individual convolutions result in excessive bellows convolution stress at and near the movable end of the arrangement. The input convolutions (i.e., those closest to the movable bellows end) are unable to accelerate the masses distributed down the bellows axial length without excessively distorting. It has not been uncommon for the first convolution to fail after only a few hundred cycles of operation.
Typical of the prior art in vacuum interrupters are U.S. Pat. Nos. 3,190,991; 3,231,704; 3,368,023; 3,555,222; and 3,627,963. That variety of prior art shows many of the variations of glass and ceramic enclosures, shield assemblies, etc. The present invention is applicable to any one of those prior art devices.
The manner in which the present invention provides an improved structure to greatly ameliorate the aforementioned problem in connection with devices such as vacuum and gas-filled interrupters will be understood as this description proceeds.